If you want to know who to blame for the government shutdown, it is worth reading up on Club for Growth, an ultraconservative group that takes pride in helping to elect the most uncompromising voices in Congress.

Look at Texas Senator Ted Cruz, whose all-night filibuster fired the first shot in the current stalemate. Back in 2010, Cruz was a little-known candidate — until Club for Growth poured more than $5 million into his campaign.

Utah Senator Mike Lee, who launched the “Don’t Fund It” website against the Affordable Care Act with Cruz, also owes his political success to the club, which engineered the ambush at the Republican primary caucus that unseated longtime incumbent Republican Bob Bennett, who committed the sin of supporting universal health insurance.

The club also nurtures the irreverent upstarts in the House who have developed an “Oedipus” complex about House Speaker John Boehner, including Steve King of Iowa, who demanded that Boehner take a “blood oath” to include defunding Obamacare in every single appropriations bill; and Tim Huelskamp of Kansas, who has pledged to vote against raising the debt ceiling unless Obamacare is curbed.

So what exactly is the club?

Most people think of it as a pro-business membership organization, formed in 1999 by a libertarian-leaning Wall Street executive who wanted a system for vetting candidates against strict free-market, anti-tax standards. Like Emily’s List, the club took $1,000 donations from members and bundled them to support specific candidates.

But at the same time, the group waged a quiet campaign to remove campaign finance restrictions. Its executive director, David Keating, filed a test case lawsuit against the FEC called SpeechNow. Just as Citizens United opened the door for unlimited political spending by unions and corporations, SpeechNow paved the way for nonprofit groups like the club to raise unlimited money. Super PACs were born. Club for Growth Action, one of the nation’s first super PACs, is the eighth largest, collecting $18 million in 2012. But that pales in comparison to the $390 million collected by the Republican National Committee. So how does the club have such influence?

The club’s real potency lies in how these funds are spent. The club funnels most of its money into taking down Republican incumbents who are not deemed free-market enough. Two years ago, it spent $3 million for Republican candidates, and $9 million against them.

Financing primary upsets in safe Republican districts is a cheap way to change the face of Congress. The club only spent about $200,000 on Mike Lee’s race in Utah. That race not only got the club a more ideologically pure member of Congress, it sowed fear among the members who kept their seats.

Run afoul of the club in a safe Republican district, and Glenn Beck will hear God whisper the name of your rival in his ear.

The club’s strategy of attacking some of the most beloved veterans in the Republican Party has prompted critics to call it everything from “a cancer” to “cannibals” to the “ideology police.”

But fear turns out to be a far more potent motivator than love or loyalty.

Norman Ornstein, a political researcher at the American Enterprise Institute, estimates that the club has only about 40 “true believers” in the House.

“But you have another 100 who are scared to death of the 40, and of the outside groups like the Club for Growth who will go after them,” he said.

As the number of “safe” districts has grown, due in part to gerrymandering, the number of races the club can win has only increased.

So it is fear, more than anything else, that herded the GOP majority in the House away from Boehner’s budget comprise. The masterminds of the shutdown, which include the club, the Koch brothers, and a host of other far-right entities, have made a pact to punish anyone who votes to end it too soon.

The irony is that the club doesn’t even pretend to be loyal to the Republican Party.

“Our purpose is not to elect Republicans,” said spokesman Barney Keller, but rather to roll back government spending.

When will the GOP realize that the club isn’t really playing for their team?